response of corneal hysteresis and central corneal thickness following clear corneal cataract...

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Introduction Corneal hysteresis (CH) and central corneal thickness (CCT) are important factors reflecting the biomechanical properties of the cornea (Kotecha 2007; Luce 2005). Whereas CH pre- dominantly reflects the viscous proper- ties of the cornea (Kotecha 2007), the CCT parameter is correlated with cor- neal elasticity (Kotecha 2007; Pepose et al. 2007). Until recent years, CCT was the only factor that could be mea- sured easily in vivo. With the innova- tion of ocular response analyzer (ORA) (Reichert Ophthalmic Instru- ments, Buffalo, NY, USA), a new metric, CH was defined and its influ- ence needs further evaluation. Recent studies (Hager et al. 2007a; Kucumen et al. 2008) have demon- strated a reduction in CH in the imme- diate postoperative period following clear corneal cataract surgery. In addi- tion, the swelling effect of cornea exposed to phacoemulsification ultra- sound energy is well documented (Lundberg et al. 2005; Salvi et al. 2007). The purpose of our study is to explore the combined response of CCT and CH following cataract surgery and how this is correlated with phaco- emulsification energy. In addition, we investigated the changes of CH and CCT following routine clear corneal cataract surgery and assessed the effect of phaco energy on these parameters. Response of corneal hysteresis and central corneal thickness following clear corneal cataract surgery Artemios Kandarakis, 1 Vasileios Soumplis, 1 Michalis Karampelas, 1 Ioannis Koutroumanos, 1 Christos Panos, 1 Stylianos Kandarakis 2 and Dimitrios Karagiannis 1 1 Ophthalmiatrion Eye Hospital of Athens, Athens, Greece 2 Weill Cornell Medical College, New York, NY, USA ABSTRACT Purpose: To evaluate the effect of routine phacoemulsification in corneal viscoelas- tic properties determined by corneal hysteresis (CH) and central corneal thickness (CCT) and to explore the impact of phaco energy on the above parameters. Methods: Forty-one eyes of 41 patients undergoing cataract surgery were enrolled in this prospective study. CH and CCT were measured preoperatively, 1 day and 1 week postoperatively. CCT measurement was performed using a non-contact optical pachymeter followed by ocular response analyzer (ORA) examination. In- traoperatively ultrasound time, average phaco power and effective phaco time (EPT) were recorded. Results: Mean CH was 10.05 ± 1.86 mmHg preoperatively, 8.25 ± 1.85 mmHg 1 day and 9.12 ± 1.37 mmHg 1 week postoperatively (p < 0.001). The mean CCT was 534 ± 37.33 lm preoperatively, 592.22 ± 46.34 lm 1 day and 563.21 ± 49.84 lm 1 week postoperatively (p < 0.001). CCT and CH were sta- tistically significantly correlated preoperatively (p = 0.01, r = 0.396). This corre- lation was not sustained on the first postoperative day (p = 0.094, r = 0.265) and was re-established 1 week postoperatively (p = 0.002, r = 0.568). On the first postoperative day, the CCT increase was positively correlated with EPT (p = 0.009, r = 0.404), which was not found between CH change and EPT. Conclusion: Structural corneal alterations following cataract surgery resulted in a statistical change in CH and CCT. These two parameters responded in a different manner that clearly demarcates their different nature. On the first postoperative day, CCT increase was correlated at a statistically significant level with intraoper- ative EPT. This correlation was not found with CH reduction. Other factors, besides cornea oedema or phacoemulsification energy, could be responsible for this CH modification. Key words: cataract surgery – central corneal thickness – corneal hysteresis – effective phaco time – phacoemulsification Acta Ophthalmol. ª 2011 The Authors Acta Ophthalmologica ª 2011 Acta Ophthalmologica Scandinavica Foundation doi: 10.1111/j.1755-3768.2010.02078.x Acta Ophthalmologica 2011 1

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Page 1: Response of corneal hysteresis and central corneal thickness following clear corneal cataract surgery

Introduction

Corneal hysteresis (CH) and centralcorneal thickness (CCT) are importantfactors reflecting the biomechanicalproperties of the cornea (Kotecha2007; Luce 2005). Whereas CH pre-dominantly reflects the viscous proper-ties of the cornea (Kotecha 2007), theCCT parameter is correlated with cor-neal elasticity (Kotecha 2007; Peposeet al. 2007). Until recent years, CCTwas the only factor that could be mea-sured easily in vivo. With the innova-tion of ocular response analyzer(ORA) (Reichert Ophthalmic Instru-ments, Buffalo, NY, USA), a newmetric, CH was defined and its influ-ence needs further evaluation.

Recent studies (Hager et al. 2007a;Kucumen et al. 2008) have demon-strated a reduction in CH in the imme-diate postoperative period followingclear corneal cataract surgery. In addi-tion, the swelling effect of corneaexposed to phacoemulsification ultra-sound energy is well documented(Lundberg et al. 2005; Salvi et al.2007). The purpose of our study is toexplore the combined response of CCTand CH following cataract surgeryand how this is correlated with phaco-emulsification energy. In addition, weinvestigated the changes of CH andCCT following routine clear cornealcataract surgery and assessed the effectof phaco energy on these parameters.

Response of corneal hysteresisand central corneal thicknessfollowing clear corneal cataractsurgery

Artemios Kandarakis,1 Vasileios Soumplis,1 MichalisKarampelas,1 Ioannis Koutroumanos,1 Christos Panos,1

Stylianos Kandarakis2 and Dimitrios Karagiannis1

1Ophthalmiatrion Eye Hospital of Athens, Athens, Greece2Weill Cornell Medical College, New York, NY, USA

ABSTRACT

Purpose: To evaluate the effect of routine phacoemulsification in corneal viscoelas-

tic properties determined by corneal hysteresis (CH) and central corneal thickness

(CCT) and to explore the impact of phaco energy on the above parameters.

Methods: Forty-one eyes of 41 patients undergoing cataract surgery were enrolled

in this prospective study. CH and CCT were measured preoperatively, 1 day and

1 week postoperatively. CCT measurement was performed using a non-contact

optical pachymeter followed by ocular response analyzer (ORA) examination. In-

traoperatively ultrasound time, average phaco power and effective phaco time

(EPT) were recorded.

Results: Mean CH was 10.05 ± 1.86 mmHg preoperatively, 8.25 ± 1.85 mmHg

1 day and 9.12 ± 1.37 mmHg 1 week postoperatively (p < 0.001). The mean

CCT was 534 ± 37.33 lm preoperatively, 592.22 ± 46.34 lm 1 day and

563.21 ± 49.84 lm 1 week postoperatively (p < 0.001). CCT and CH were sta-

tistically significantly correlated preoperatively (p = 0.01, r = 0.396). This corre-

lation was not sustained on the first postoperative day (p = 0.094, r = 0.265) and

was re-established 1 week postoperatively (p = 0.002, r = 0.568). On the first

postoperative day, the CCT increase was positively correlated with EPT

(p = 0.009, r = 0.404), which was not found between CH change and EPT.

Conclusion: Structural corneal alterations following cataract surgery resulted in a

statistical change in CH and CCT. These two parameters responded in a different

manner that clearly demarcates their different nature. On the first postoperative

day, CCT increase was correlated at a statistically significant level with intraoper-

ative EPT. This correlation was not found with CH reduction. Other factors,

besides cornea oedema or phacoemulsification energy, could be responsible for this

CH modification.

Key words: cataract surgery – central corneal thickness – corneal hysteresis – effective phaco

time – phacoemulsification

Acta Ophthalmol.ª 2011 The Authors

Acta Ophthalmologica ª 2011 Acta Ophthalmologica Scandinavica Foundation

doi: 10.1111/j.1755-3768.2010.02078.x

Acta Ophthalmologica 2011

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Page 2: Response of corneal hysteresis and central corneal thickness following clear corneal cataract surgery

Patients and Methods

This prospective, non-randomizedstudy involved patients with age-related cataract planned for routinephacoemulsification and intraocularlens (IOL) implantation. A total of 41patients, 17 men and 24 women,underwent an uneventful clear cornealcataract surgery with phacoemulsifica-tion by the same experienced surgeon(AK). There were no ocular pathologyof note and no history of previousocular injury. None of these patientshad undergone ocular surgery or werecontact lens wearers. None of thepatients were suffering from glaucomaor using any topical medication.

Preoperatively, a full eye examina-tion was performed, including visualacuity measurement, biomicroscopy ofthe anterior and posterior segmentand tonometry. CCT measurementwas first performed using a non-con-tact optical pachymeter (HAAG-STREIT AG, Koeniz, Switzerland)followed by ORA examination. CCTand CH measurements were repeated3 and 4 times, respectively, and themean values were recorded.

Mydriasis was obtained before sur-gery with tropicamide hydrochloride1% (Tropixal, Demo SA, Greece) andphenylephrine hydrochloride 5%(Phenylephrine, Cooper SA, Greece).After topical anaesthesia with dropsof proparacaine HCl 0.5% (Alcaine,Alcon Laboratories Hellas, Maroussi,Athens, Greece), a clear cornea 2.75-mm incision was performed. Sodiumhyaluronate (Provisc, Alcon Labora-tories Inc.) was used as viscoelasticsubstance. Phacoemulsification of thenucleus was performed with an AlconInfinity unit, using phaco-chop tech-nique, followed by the aspiration ofcortical remnants and polishing of thecapsular bag. A foldable one-pieceacrylic intraocular lens (Corneal Qua-trix, Corneal, France) was implantedin the capsular bag using an injector.The viscoelastic substance was aspi-rated meticulously using an irriga-tion ⁄ aspiration tip. Main incision wasleft sutureless.

Intraoperatively, ultrasound time,average phaco power and effectivephaco time (EPT) were recorded. EPTis a measure of the total ultrasoundenergy used during the operation andwas calculated by multiplying the totalultrasound time by the average phaco

power used. CH and CCT were alsomeasured 1 day and 1 week postoper-atively in the same manner as preop-eratively.

Paired sample t-test and Pearsoncorrelation analysis were used for sta-tistical analysis. Values are presentedas mean ± standard deviation. Alltests were 2-sided, and p values of0.05 or less were considered statisti-cally significant.

The Ethical Board of our hospitalapproved the study, and after detailedexplanation, informed consent wasobtained from each patient prior toexamination.

Results

Forty-one eyes of 41 patients under-going clear corneal cataract surgerywere enrolled in this study. Allpatients were Caucasians, 17 weremen and 24 were women; mean agewas 73.9 ± 7.4 years. Twenty-two

right and 19 left eyes were operatedon and analysed. Mean CH decreasedfrom 10.05 ± 1.86 mmHg before sur-gery to 8.25 ± 1.85 mmHg 1 daypostoperatively, and it then slightlyrose to 9.12 ± 1.37 mmHg 1 weekpostoperatively (Fig. 1). The meanCCT was 534 ± 37.33 lm preopera-tively, 592.22 ± 46.34 lm 1 day post-operatively and 563.21 ± 49.84 lm1 week postoperatively (Fig. 2). Wedid not find any correlation betweenage and the preoperative values ofCCT and CH (p = 0.142, p = 0.114,respectively). Mean phaco time was115.95 ± 73.62 s, and mean averagepower was 18.35 ± 5.22%. MeanEPT was 20.66 ± 11.88 s.

Statistically significant differencesbetween preoperative values and theones in the first postoperative day andin 1 week postoperatively were foundfor both CH and CCT (p < 0.05).

Pearson correlation analysis showedstatistically significant correlation

Fig. 1. Graph showing corneal hysteresis (CH) before clear corneal cataract surgery, on the first

postoperative day as well as 1 week after surgery. Vertical bars: 95% confidence interval.

Fig. 2. Graph showing central corneal thickness (CCT) before surgery, on the first postopera-

tive day after clear corneal cataract surgery as well as 1 week after surgery. Vertical bars: 95%

confidence interval.

Acta Ophthalmologica 2011

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Page 3: Response of corneal hysteresis and central corneal thickness following clear corneal cataract surgery

between preoperative CH and preop-erative CCT (p = 0.01, r = 0.396).This correlation was not sustained onthe first postoperative day (p = 0.094,r = 0.265) but it was re-established1 week postoperatively (p = 0.002,r = 0.568).

On the first postoperative day, theCCT increase was positively correlatedwith EPT (p = 0.009, r = 0.404)(Fig. 3). This correlation was notrecorded 1 week later (p = 0.104,r = 0.326). There was not any statisti-cally significant correlation betweenEPT and CH changes neither on thefirst postoperative day nor 1 weeklater. (p = 0.689, r = )0.065 andp = 0.390, r = )0.176, respectively).In addition, on the first postoperativeday, the corneal oedema as repre-sented with CCT increase was not cor-related with the simultaneouslydetected CH reduction (p = 0.429,r = 0.127).

Discussion

The introduction of CH has been asignificant step in the process of creat-

ing a new method to determine thebiomechanical properties of the cor-nea in vivo. It has been shown thatCH is independently associated withprogressive glaucoma damage (Cong-don et al. 2006). Shah et al. (2006)suggested that CH may be helpful forlong-term monitoring of glaucomaand other diseases of the cornea whereintraocular pressure (IOP) is of criticalrole, because it provides further infor-mation about the biomechanics of thecornea, beyond that of CCT (Hageret al. 2007b).

Furthermore, CH has already beenshown to be higher in normal incomparison with keratoconic eyes(Shah et al. 2007) and two recent sep-arate studies had shown that afterLASIK surgery, CH was significantlyreduced (Ortiz et al. 2007; Peposeet al. 2007).

The aim of our study was toexplore the effect of uncomplicatedphacoemulsification in corneal visco-elastic properties determined by CHand CCT and to evaluate the effect ofphaco energy on these two parame-ters. All measurements were obtained

during office hours because it hasbeen shown that CH and CCT arealmost constant throughout the day(Laiquzzaman et al. 2006).

According to the literature, CCTincreases after clear corneal phaco-emulsification (Lundberg et al. 2005;Salvi et al. 2007). On the first postop-erative day, we found a statisticallysignificant increase in CCT, whichremained 1 week after surgery. Themean preoperative value of CH in ourgroup (10.05 ± 1.86 mmHg) was sim-ilar to the range of average valuesfound in literature: 9.6 mmHg in 339normal eyes (Luce 2005) and10.6 ± 2.3 mmHg in 156 normal eyes(Hager et al. 2007b). CH demonstrateda statistically significant decrease onthe first postoperative day. One weekafter surgery, CH showed an ascendingcourse but remained statistically signifi-cantly lower than the baseline. Compa-rable results were recently reported bytwo other studies (Hager et al. 2007a;Kucumen et al. 2008). Hager et al.(2007a) found that at day 1 after clearcorneal cataract surgery, preoperativeCH is diminished from 10.35 to 9.2. Inanother study, 1 week postoperatively,CH was also significantly lower thanthe preoperative values showing adecrease from 10.36 to 9.65 (Kucumenet al. 2008). In this study, Kucumenet al. measured CH 3 months afterphacoemulsification and found no sta-tistically significant difference from thepreoperative values. Based on our find-ings and using a linear hypothesis, weestimated that if CH continued to riseat the same rate, it would reach the pre-operative value in approximately14 days following surgery (Fig. 4).Although we appreciate that linearrelationships in human tissue are rare,this finding serves only as an approxi-mation, because the actual rate of CHrecovery has not yet been defined.

Previous studies (Lu et al. 2007;Luce 2005; Shah et al. 2006) haveinvestigated the relationship betweenCCT and CH and found that thesetwo parameters correlate with eachother. In agreement with these find-ings, we showed that there was a posi-tive correlation preoperatively, whichceased to exist in the first postopera-tive day. This correlation wasre-established 1 week later, althoughboth CH and CCT were still statisti-cally significantly different from theirbaseline values. This clearly demar-

Fig. 4. Graph showing, hypothesis based, linear ascending course of corneal hysteresis (CH)

after the first week.

Fig. 3. Correlation of central corneal thickness (CCT) increases on the first postoperative day

and effective phaco time (EPT) (CCT1: central corneal thickness before surgery, CCT2: central

corneal thickness 1 day after surgery).

Acta Ophthalmologica 2011

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Page 4: Response of corneal hysteresis and central corneal thickness following clear corneal cataract surgery

cates the different nature of these twoparameters, a difference that emergesfrom their dissimilar reaction to thesame event. In support to our find-ings, Lu et al. (2007) measured CHduring corneal swelling induced bycontact lens wear with eye closure.During this experiment, the alterationof CCT was not associated withchanges of CH at a statistically signifi-cant level. This signifies that, like ourfindings, CCT and CH behave in adifferent way under corneal stress con-ditions.

Yao et al. (2006) showed that cor-neal oedema 1 day postoperativelyincreased in relation to greater EPT.Similar to this study, our results provethat CCT difference on the first post-operative day was correlated at a sta-tistically significant level with EPT.However, Ermiss et al. (2003) foundthat such a correlation does not exist.One possible explanation for this dis-crepancy could be that we used acohesive viscoelastic agent rather thana dispersive one.

Regarding CH, we did not find anystatistically significant correlationbetween EPT and CH differences. Toour knowledge, this is the first studythat demonstrates such a result, whichin conjunction with the above-men-tioned behaviour of CCT highlights thedifferent response of those two param-eters to phacoemulsification. One pos-sible explanation for this finding couldbe that the reduction in CH is influ-enced by multiple factors beyond phac-o energy. According to previousstudies (Hager et al. 2007a; Kucumenet al. 2008), CH reduction has beenattributed to corneal oedema, whichlowers the damping capacity of the cor-nea. In our study, we found no correla-tion between corneal oedema, asrepresented by CCT increase and CHreduction. Changes of CH have alsobeen shown to occur in patients under-going pars plana vitrectomy (PPV) toan even higher extent (Hager et al.2008), although cornea was not directlymechanically affected during the PPVprocedure. Because CH has beenhypothesized to reflect the global ocu-lar biomechanics and not just the cor-nea’s (Congdon et al. 2006; Dupps2007), the cause of this CH modifica-tion could be attributed to the effect ofcataract surgery to the eye as a whole.Possible elements of this effect could be

the clear corneal incision or themechanical stress of phacoemulsifica-tion on the globe.

In conclusion, structural cornealalterations after clear cornea cataractsurgery lead to a compromise of itsbiomechanical properties as demon-strated by a statistically significantreduction in CH. CCT and CHrespond in a different manner aftercataract surgery. Other factors, besidescorneal oedema or phacoemulsificationenergy, could be responsible for thisCH modification. Further studiesshould be undertaken to elucidate thetime period where CH returns to itspreoperative values as well as the fac-tors that influence this behaviour.

Acknowledgement

There has been no financial support(grants) for this study. None of theauthors have any kind of financial orproprietary interest in the manuscript.

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Received on May 28th, 2010.

Accepted on November 14th, 2010.

Correspondence:

Dr Artemios Kandarakis, MD, FACS

Ophthalmiatrion Eye Hospital of Athens

1st Ophthalmology Department

Sina 2

Athens, 106 72

Greece

Tel: 0030 6944335334

Fax: 0030 210 8130031

Email: [email protected]

Acta Ophthalmologica 2011

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